The present invention relates generally to sampling systems for mass spectrometers and, more specifically, to an environmental sampler for a mass spectrometer that allows for controlled introduction of small amounts of fluids or gases into the vacuum system of the mass spectrometer under severe environmental conditions.
There have been diverse types of samplers proposed for mass spectrometers. For example, U.S. Pat. No. 4,201,913 to Bursack et al. discloses an apparatus for introducing a gaseous sample into a mass spectrometer which includes a hollow antechamber or cavity disposed between the sample stream and a high vacuum enclosure. Orifice openings are provided in the antechamber which allow the antechamber to communicate both with the high vacuum enclosure and the sample stream. An electrically operated pulsed valve is used to admit a series of small volumes of sample by pulses of controlled duration and frequency such that the sample flow from the antechamber into the high vacuum enclosure can be made to resemble one of essentially constant flow.
U.S. Pat. No. 4,386,852 to Cassidy et al. discloses a phase synchronization apparatus useful for synchronizing the sample signal and the demodulation signal at a spectrometer, which included a stepper motor the position of which is controlled so that the desired phase synchronization is ensured.
U.S. Pat. No. 4,562,351 to Atherton et al. discloses a mass spectrometer having a sample insertion probe on which a reference compound and an unknown sample can be simultaneously introduced without mixing into a field ionization or ion or neutral particle bombardment ion source. An insulated support is mounted by a parallel hinge on the end of a probe shaft. Two or more separated segments or emitter wires, one carrying the unknown sample, and another carrying the reference compound, are mounted on a base member which is fitted to the support. A drive shaft, concentric with an outer probe shaft, has an eccentric peg on the end, which engages with a cam on the support, so that rotation of the drive shaft results in an oscillating motion of the segments or emitters, alternately positioning them in the optimum position for ionization. A spectrum of the sample or the reference compound can be obtained when required by selecting the appropriate position of the drive shaft. Rotation of the drive shaft may be controlled by a servo-mechanism and a computer. As a result, improved accuracy of mass measurement of peaks in the mass spectrum of the sample is achieved.
U.S. Pat. No. 4,590,165 to Gilles et al. disclosed an automatic sampling method for introducing a diluted viscous sample into an instrument for analysis for trace elements. The automatic sampling system includes a tube assembly, a member for mounting the tube assembly in proper relation, means for maintaining, between sampling, the free end of the tube assembly in a cleaning solution, and means for inserting the free end of the tube assembly into a sample contained within a container. Preferably, the instrument is a spectrometer, the samples are organic and aqueous samples, such as oils, brines, sludges, plating solutions and the like, and the trace elements include wear metals and also other elements, such as calcium, barium, zinc, sodium, magnesium, boron, phosphor and the like.
U.S. Pat. No. 4,601,211 to Whistler discloses a multi-port valve using a flexible sample tube to selectively intercept gases flowing from inlet ports into a common manifold space. The manifold space is placed under sufficient vacuum to ensure that gas samples will be selectively received by the sample tube when the sample tube is placed in close proximity to the selected inlet port to be sampled. The sample tube is arranged so that gases to be sampled from the selected port wash over the entrance end of the sample tube so that contaminated or mixed gases from the manifold space are prevented from entering the sample tube. The sample tube is mounted to pivot inside the valve body to selectively align the sample tube with the inlet ports. The valve body may be sealed by a cover through which the valve guide is driven to rotate by a magnetic coupling, or by a bearing seal through which the sample tube guide projects. The sample guide may be rotated in a stepwise fashion by a stepper motor for slow collection rates, or may be rotated quickly by a motor for rapid sampling. Magnetic detectors or a shaft decoder may be used to monitor the position of the sample tube guide. The multi-port valve may be used in a system in which a measuring device such as a mass spectrometer and a data system are used.
U.S. Pat. No. 4,879,458 to Brunfeldt discloses an automated sample inlet system for sequentially introducing a plurality of indium encapsulated samples into a mass spectrometer wherein the samples are placed in a micro tube and loaded into a circular carousel under a vacuum bell jar maintained at ambient temperature. The samples are systematically advanced by rotating the carousel resulting in each sample sequentially falling through a delivery tube containing an inverted ball valve into a sample vaporizing chamber within an oven. An additional pair of sapphire ball valves in communication with the glass vaporizing chamber are sequentially opened and closed in a preprogrammed manner along with the opening and closing of the thermal inverted ball valve and the indexing of the carousel such as to automatically evacuate the glass inlet system within the oven, introduce a new sample and vaporize it and then inject this vapor into a mass spectrometer. Such a system is useful in running large numbers of mass spectrometer analyses of hydrocarbon liquids and the like.
U.S. Pat. No. 5,397,989 to Spraul et al. discloses an NMR spectrometer for the measurement of liquid samples having a probe head exhibiting an upper and a lower support, a connector for a feed conduit for the introduction of a liquid sample into the spectrometer and a connector for a drain conduit for the drainage of the liquid sample out of the spectrometer, a sample tube, arranged between the upper and lower supports, for the acceptance of the fluid sample, whereby the one end of the sample tube is connected to the connector for the feed conduit and the other end to the connector for the drain conduit, exhibits, coaxially to the sample tube, a further tube for the acceptance of a calibration fluid which, on one end, is connected to an additional connector for a feed conduit to introduce the calibration fluid into the spectrometer and, on its other end, to an additional connector for a drain conduit to drain the calibration fluid out of the spectrometer. In this manner, it is possible to measure the sample fluid in a simple fashion, without the previous mixing of additives and, subsequent to the measurement, to regain the sample fluid in its original state, while allowing for the introduction of a calibration fluid for field stabilization and for the quantitative comparison of line intensities.
U.S. Pat. No. 5,705,928 to Haner discloses a sample delivery system for flow-through NMR analysis which utilizes pressurized gas as a means for conveying a sample into and out of an NMR spectrometer. Two sources of gas pressure, a forward pressure and a back pressure, oppose the sample within the tubing of the sample delivery system and the tubing of the flow-through system which are operatively coupled together. Conveyance of a sample in any direction within the tubing is achieved by adjusting the pressure differential. Precise positioning of the sample in the magnetic field and complete removal of the sample from the NMR spectrometer when analysis is complete are achieved by using a signal processor which receives signals from the NMR detector or other detectors positioned along the length of the tubing. These signals provide an indication of the position of the sample in the tubing. The signal processor uses this information to adjust the forward and back pressure, thereby achieving the desired positioning of the sample.
U.S. Pat. No. 5,841,136 to Holle et al. discloses a system and method for the introduction of sample supports, which hold large numbers of analysis samples, into the ion source region of a mass spectrometer. The sample supports are especially intended for the ionization method using matrix-assisted desorption through laser bombardment (MALDD). The system consists of an evacuable, sealable and removable cassette which, instead of using a through-passage lock chamber with two lock valves, can be attached in a simple manner to the entrance opening for the ion source of the mass spectrometer. Only the entrance opening has a lock valve, and the expensive second lock valve in the lock chamber is no longer needed. The cassette can also be used for protected transport and for storage of the sample supports, and in particular for storage of the samples under protective gas or vacuum.
U.S. Pat. No. 6,177,991 to Okuda discloses a measuring device such as a spectrometer which uses an automatic sample changer for carrying a plurality of samples. The automatic sample change may include a rotary circular disk rotatable around its central shaft by a stepping motor for changing positions of the samples which are positioned in a circle around the central shaft of the disk. A memory device preliminarily storing control data for each of different kinds of automatic sample changers is provided. The automatic sample changer, when connected to a control unit in the main body, serves to receive control signals for controlling motions of the motor and to transmit data stored in the memory device through a connector. The main body of the measuring device contains a control unit which serves to read out the control data from the memory device, to use the received control data to generate the control signal and to transmit the generated control signal to the automatic sample changer.
U.S. Pat. No. 6,182,012 to Kenny discloses a manipulator apparatus, system and method for measuring analyses present in sample tubes. The manipulator apparatus includes: a housing having a central bore with an inlet end and outlet end; a plunger mechanism with at least a portion thereof slideably disposed for reciprocal movement within the central bore, the plunger mechanism having a tubular gas channel with an inlet end and an outlet end, the gas channel inlet end disposed in the same direction as said inlet end of the central bore, wherein the inlet end of said plunger mechanism is adapted for movement so as to expel a sample tube inserted in the bore at the outlet end of the housing, and the inlet end of the plunger mechanism is adapted for connection to a gas supply; a first seal disposed in the housing for sealing between the central bore and the plunger mechanism; a second seal disposed at the outlet end of the housing for sealing between the central bore and a sample tube; a holder mounted on the housing for holding the sample tube; and a biasing mechanism for returning the plunger mechanism to a starting position.
U.S. Pat. No. 6,190,316 to Hirabayashi discloses a living body fluid analyzing system which includes a microdialysis for sending a first solution having an osmotic pressure which is substantially similar to an osmotic pressure of a body fluid into a living body and extracting a second solution from the living body. A first flow passage is provided in which the second solution from the microdialysis flows and a second flow passage is provided which mixes the second solution with an organic solution. Furthermore, there is provided a gas source and a gas flow controller which controls a flow quantity of the gas from the gas source and a third flow passage in which a gas introduced from the gas source flows. An ion source is provided having an orifice for spraying and ionizing the second solution from the second flow passage at an end of the third flow passage, and a mass spectrometer is provided for mass-analyzing the ions sprayed from the orifice.
While these prior mass spectrometer sampling devices may be suitable for the purposes for which they were designed, they would not be as suitable for the purposes of the present invention, as hereinafter described.
In accordance with the present invention, an environmental sampler for a mass spectrometer has a sampler member which is driven in reciprocation through a port in the sampler housing to allow for controlled introduction of samples of small amounts of fluids or gases into the vacuum system of an attached mass spectrometer under severe environmental conditions, such as at high pressures in great depths of water. Accurate calibration of the sampler and mass spectrometer relative to the sample is made possible by means of an internal reservoir containing a standard or reference material which is integral with the sampler of the present invention.
In a preferred embodiment, the sampler member is a linear rod formed with a series of recesses of predefined volumes on its forward and back ends. A computer-controlled stepper motor moves a guide rod which is aligned in parallel with and coupled to the sampler rod in a manner which minimizes any torque forces on the sampler rod. The sampler rod is driven in reciprocation to take an external sample outside of the sampler housing and a standard sample from the internal reservoir inside the housing. It is driven in forward motion (to extend outside of the pressurized housing) a predetermined number of steps within which recesses corresponding to a predetermined volume on its back end samples the internal standard reservoir and delivers the standard sample to an inlet channel of the mass spectrometer, and driven in reverse motion (to return inside the pressurized housing) within which recesses corresponding to the predetermined volume on its forward end provides the external sample to the inlet channel of the mass spectrometer.
The recesses on the sampler rod may be formed as a series of successively deeper grooves in two sets. The rod system and internal reservoir are pressure compensated to reduce any forces acting on the stepper motor. The configuration of the rod system ensures that the volume and mass of the external sample to the standard sample may be taken in small quantities in a constant ratio of approximately one to one. Hydraulic seals and O-rings are used to keep external fluids and gases from entering the sampler. The fluid samples and dissolved gases held in the recesses on the sampler rod are evaporated from its surface into the vacuum of the inlet channel communicating into the mass spectrometer.
In operation, all parts in the sampler are sealed against any detectable flow into the mass spectrometer. Flow into the sampler vacuum channel is obtained by engineering the small calibrated recesses in the sampler rod system, thereby permitting small calibrated amounts of samples to be introduced repeatably and reliably into the vacuum system of the attached mass spectrometer as the rod reciprocates back and forth. The small sampling capability reduces the pumping load on the vacuum system and permits extended in situ operation by virtue of its low power consumption. The operational pressure range (from less than one atmosphere to greater than 400 atmospheres) allows autonomous operation in a variety of water (to full ocean depths), terrestrial, and even space environments.
Due to the small sample volumes that can be reliably acquired, the initial sample temperatures can be quite high without having a serious effect on the mass spectrometer. Temperature maximums are only dictated by the choice of materials for the sampler seals and the sampler plenum parts. Management of sample temperatures in excess of 200 degrees C. is possible if high temperature polymer materials such as silicon or Teflon(TM) are used. The pressure-compensated sampler housing and rod system is also economical in cost to manufacture and operate.
The present invention further includes the use of a removable, external vacuum port to allow pumping and emptying of a waste vacuum for the mass spectrometer to ambient. A removable external sampler plenum is used to direct a flow of gas or fluid over the sampler rod from a region to be sampled.
The present invention is primarily designed to be used with an attached mass spectrometer, but can also be used in other applications where small, calibrated quantities of a sample are to be taken from an environment, such as in gas or liquid chromatography, capillary electrophoresis, or any combination of these and other analytical techniques with mass spectroscopy.